LONDON (Reuters) - Britain will soon put forward its proposal for a backstop arrangement to prevent a hard border with EU member Ireland, Prime Minister Theresa May told European Union officials on Thursday, her spokeswoman said.

May made the comments at a meeting with European Commission President Jean-Claude Juncker and European Council President Donald Tusk in the Bulgarian capital, Sofia.

“The prime minister reiterated the UK’s commitment to the joint report agreed in December. She said the proposal put forward by the European Commission in relation to the Ireland/Northern Ireland border was unacceptable,” the spokeswoman said.

“The prime minister said the UK would shortly put forward its own backstop proposal in relation to customs.”